This invention is generally directed to flash fusing processes, and more specifically the present invention relates to processes for affecting a reduction in the energy required for flash fusing while simultaneously, for example, minimizing image de-enhancement. Therefore, in one embodiment of the present invention there is provided a process for accomplishing a reduction in flash fusing energy for electrostatographic imaging systems wherein the toner particles selected are prespheroidized. With prespheroidization of the toner particles by heat spheroidization processes, for example, there results a desirable decrease in the energy required for affecting flash fusing of the developed images. The process of the present invention, therefore, is particularly useful for permitting image de-enhancement minimization and flash fusing energy reduction in electrostatographic imaging systems having incorporated therein a flash fusing device.
The formation and development of images on the surface of electrophotographic material, such as photoreceptors, for example, by electrostatic means is well known, these processes involving subjecting the photoconductive material to a uniform charge, and subsequently exposing the surface thereof to a light image of the original to be reproduced. The latent image thus formed on the xerographic photoconductive surface is developed with toner particles specifically prepared for this purpose. Thereafter the developed image can be transferred to a final support material such as paper, and affixed thereto enabling a permanent record or copy of the original. Numerous methods are known for applying the electrostatic toner particles to the electrostatic latent image, including for example, cascade development, magnetic brush development, powder cloud development, and touchdown development.
The image formed can be fixed by a number of various well known techniques including, for example, vapor fixing, radiant fixing, pressure fixing, or combinations thereof, as described, for example, in U.S. Pat. No. 3,539,161. These techniques of fixing while suitable for certain purposes suffer from some deficiencies thereby rendering their use either impractical or difficult for specific electrostatographic applications. For example, it is difficult to construct an entirely satisfactory radiant fuser which has high efficiency, can be easily controlled, and has a desirable short warm-up time. Also, radiant fusers sometimes burn or scorch the support material. Somewhat similar problems including, for example, image offsetting and undesirable resolution degradation are present with pressure fusing methods. Additionally, with these processes, consistently desirable permanent images are not obtained. Further, although vapor fixing has advantages, one of its main disadvantages is that a toxic solvent is used, therefore, in many situations this method becomes commercially unattractive in view of health hazards associated therewith. Also, in vapor fixing equipment and apparatus to sufficiently isolate the fuser from the surrounding area is very complex, costly, and difficult to operate.
Many of the modern electrostatographic reproducing apparatuses, which are capable of producing copies at an extremely rapid rate, created the need for the development of new materials and processing techniques. With these systems, radiant flash fusing is one of the preferred fixing processes selected in that the energy which is emitted in the form of electromagnetic waves is immediately available, and requires no intervening medium for its propogation. Although an extremely rapid transfer of energy between the source and the receiving body is provided with the flash fusing process, a problem encountered with this process resides in obtaining an apparatus which can fully and efficiently utilize a preponderance of the radiant energy emitted by the source during a relatively short flash. The toner image in these systems usually comprises a relatively small percentage of the total area of the copy receiving the radiant energy causing some of the energy generated to be wasted as it is transmitted to the image, or is reflected away from the fusing areas. Furthermore, many of the toner compositions currently available, particularly colored toner compositions, contain pigments which do not absorb energy in the near infrared region of the spectrum thereby necessitating the supply of larger amounts of energy to these compositions in order to affect fusing. Moreover, many of the known colored toner compositions contain pigments therein which do not absorb energy in the near infrared and/or ultraviolet region of the spectrum, thus only about 33 percent of the spectral energy generated, for example, from presently used Xenon lamps is absorbed by the colorants contained in the toner composition.
Generally, radiation energy emitted from a Xenon flash lamp, or similar source, is absorbed by the pigment or dye contained in the toner composition; and thereafter, this energy is converted to thermal energy by a radiationless decay process enabling heat generation causing the toner particles to fuse. The flash energy used is absorbed in a layer of toner of finite thickness adjoining the outer toner surface, with absorption being greatest at the surface. This energy also constantly decreases with increasing distance from the outer toner surface. Also, the flash generated is of very short duration, on the order of about one millisecond, and consequently the toner regions very close to the surface are heated to a much higher temperature than the toner mass as a whole.
Examples of known flash fusing systems that may be selected for the present invention include those as described in U.S. Pat. Nos. 3,529,125; 3,903,394; and 3,474,223, the disclosure of each of these patents being totally incorporated herein by reference. Generally, the flash fuser selected contains a Xenon lamp, the output of the lamp being primarily in the visible and near infrared wavelengths of the regions. The output of the flash lamp is measured by joules using the capacitor bank energy in accordance with the formula 1/2 CV.sup.2 wherein C is capacitance and V is the voltage. One of the main advantages of such a flash fuser over other known methods of fusing is, as indicated herein, that the energy propagated in the form of electromagnetic waves is immediately available, and no intervening source is needed. Also, such flash fusing systems do not require long warm-up periods, and the energy does not have to be transferred through a relatively low conductive or corrective heat transfer mechanism.
Moreover, a percentage of the flash fusing energy apparently is consumed by the toner particles to affect spheroidization thereof, a rather surprising finding as illustrated hereinafter. Thus, for example, it is believed that about 2 joules of energy are initially consumed by the toner particles to affect spheroidization thereof. In accordance with the process of the present invention, this problem is eliminated. Additionally, the process of the present invention enables image deenhancement minimization. By de-enhancement is meant the reduction of image density caused by, for example, the spheroidization and coalescence of the toner particles during the flash fusing process. This de-enhancement can be decreased somewhat and the image density improved when the toner is caused to wet the supporting substrate and spread out; that is, it becomes liquified and covers the substrate with toner particles which are prespheroidized prior to the flash fusing operation; that is, the process of the present invention, image de-enhancement, is substantially eliminated particularly for image densities equal to or less than 1.
Accordingly, there is a need for processes that will permit the efficient flash fusing of images generated in electrostatographic apparatuses. There is also a need for processes that will enable the reduction in flash fusing energy requirements. Further, there is a need for processes permitting a reduction in image de-enhancement or optical density. Furthermore, there is a need for accomplishing the prespheroidization of toner particles thereby allowing their use in electrostatic systems having incorporated therein flash fusing devices, and wherein the energy requirements thereof are significantly reduced. There is also a need for decreasing the cost and size of toner powder supplies for flash fusing; and further the reduction of image de-enhancement enables flash fusing energy reductions.
For a better understanding of the invention as well as other aspects and further features thereof, reference is had to the following drawings and descriptions.